1. Field of the Invention
The present invention relates to a novel phosphor, a process for the preparation of the same, a radiation image recording and reproducing method utilizing the same, and a radiation image storage panel employing the same. More particularly, the invention relates to a novel cerium activated rare earth halide phosphor.
2. Description of the Prior Art
There is well known a cerium activated rare earth oxyhalide phosphor (LnOX:Ce, in which Ln is at least one rare earth element selected from the group consisting of Y, La, Gd and Lu; and X is at least one halogen selected from the group consisting of Cl and Br) as a cerium activated rare earth halide phosphor. As described in Japanese Patent Provisional Publication No. 55(1980)-12144 (which corresponds to U.S. Pat. No. 4,236,078), etc., the phosphor gives emission (stimulated emission) in the near ultraviolet region when excited with an electromagnetic wave such as visible light or infrared rays after exposure to a radiation such as X-rays, cathode rays or ultraviolet rays. The phosphor is valuable as a stimulable phosphor employable for a radiation image recording and reproducing method.
The radiation image recording and reproducing method utilizing the stimulable phosphor can be employed in place of the conventional radiography utilizing a combination of a radiographic film having an emulsion layer containing a photosensitive silver salt and an intensifying screen as described, for instance, in U.S. Pat. No. 4,239,968. The method involves steps of causing a stimulable phosphor to absorb a radiation having passed through an object or having radiated from an object; sequentially exciting (or scanning) the phosphor with an electromagnetic wave such as visible light or infrared rays (stimulating rays) to release the radiation energy stored in the phosphor as light emission (stimulated emission); photoelectrically detecting the emitted light to obtain electric signals; and reproducing the radiation image of the object as a visible image from the electric signals.
In the radiation image recording and reproducing method, a radiation image is obtainable with a sufficient amount of information by applying a radiation to the object at a considerably smaller dose, as compared with the conventional radiography. Accordingly, this method is of great value, especially when the method is used for medical diagnosis.
For other stimulable phosphors employable in the above-described method, there have been known a divalent europium activated alkaline earth metal fluorohalide phosphor (M.sup.II FX:Eu.sup.2+, in which M.sup.II is at least one alkaline earth metal selected from the group consisting of Mg, Ca and Ba; and X is at least one halogen selected from the group consisting of Cl, Br and I); an europium and samarium activated strontium sulfide phosphor (SrS: Eu,Sm); an europium and samarium activated lanthanum oxysulfide phosphor (La.sub.2 O.sub.2 S:Eu,Sm); an europium activated barium aluminate phosphor (BaO.Al.sub.2 O.sub.3 :Eu) an europium activated alkaline earth metal silicate phosphor (M.sup.2+. SiO.sub.2 :Eu, in which M.sup.2+ is at least one alkaline earth metal selected from the group consisting of Mg, Ca and Ba), and the like.